document.rb

  validates_attachment_content_type :attachment, {
    :content_type => 
      # DOC
      %w( application/msword application/doc appl/text application/vnd.msword application/vnd.ms-word application/winword application/word application/x-msw6 application/x-msword ) +
      # DOCX
      %w( application/vnd.openxmlformats-officedocument.wordprocessingml.document ) + 
      # ODT
      %w( application/vnd.oasis.opendocument.text application/x-vnd.oasis.opendocument.text ) +
      # SXW
      %w( application/vnd.sun.xml.writer ) + 
      # RTF
      %w( application/rtf application/x-rtf text/rtf text/richtext application/msword application/doc application/x-soffice ) + 
      # TXT
      %w( text/plain application/txt browser/internal text/anytext widetext/plain widetext/paragraph ) +
      # CSV
      %w( text/comma-separated-values text/csv application/csv application/excel application/vnd.ms-excel application/vnd.msexcel text/anytext ) +
      # HTM and HTML
      %w( text/html text/plain ) +
      # PPT and PPS
      %w( application/vnd.ms-powerpoint application/mspowerpoint application/ms-powerpoint application/mspowerpnt application/vnd-mspowerpoint application/powerpoint application/x-powerpoint application/x-m ) +
      # ODP
      %w( application/vnd.oasis.opendocument.presentation application/x-vnd.oasis.opendocument.presentation ) +
      # XLS and XLSX
      %w( application/vnd.ms-excel application/msexcel application/x-msexcel application/x-ms-excel application/vnd.ms-excel application/x-excel application/x-dos_ms_excel application/xls application/vnd.openxmlformats-officedocument.spreadsheetml.sheet) +
      # ODS
      %w( application/vnd.oasis.opendocument.spreadsheet application/x-vnd.oasis.opendocument.spreadsheet )
  }